I have always liked the Shell Helix range of oils for my Alfa 1.7 8V, among other things they do have great cleaning characteristics, as I am always amazed at how clean the inside of my engine is when I do any significant work.
I used to always use semi synthetic 10W40 grade oil but found small flecks of aluminium (not bearings) at the bottom of the pan after every change. I have since changed to a thicker 15W50 grade shell helix super mineral oil, and the number of flecks in the oil after a change are significantly less. Hence, what Im trying to say is that these engines are by no means young engines anymore and the tolerances were never like what they are today. I think it is best to run a slightly thicker oil than recommended, ie 15W50, as a thicker oil will have a thicker coat on the internal parts and fill the 'gaps' between parts, ie worn areas and larger tolerances and give better protection. Just my two cents.
Also oil change intervals of 5000kms should be stuck to with a good quality filter (of appropriate size) replaced at all oil changes.
I use shell fully synthetic 10w40 as it leaves fewer deposits in engine and effectivley cleans engine as well as ruuning a little cooler.
google synthetics on the web there is a lot of info
There is a myth that fully synthetic in an older engine will strt to seep through seals but I haven't found this on either of my boxer engined beasties.
alfa 33 1.7 ti
I use castrol 10w60 sythetic R, but its a new engine too so bit different too. But with my 8v i have to agree with the shell synthetic range they are very good too. Just stay away from those *** lightweight oils
Alfa recommend 10W-50. Try and stick to that. 15W-50 good too. If you live in a cold climate, 10W-40 would be good.
Apparently the new SM oil specification specifies greatly less thiosphosphates than the older spec oils. Some owners of older cars are reporting severe valve train damage after running these oils. I don't know if this affects boxers.